Resolution of racemic alpha-hydroxy-beta,beta-dimethyl-gamma- butyrolactone



3,541,139 RESOLUTION OF RACEMIC Ot-HYDROXY' fi,fl-DIMETHYL-'y-BUTYROLACTONE Robert Winterbottom, New City, N.Y., and William M.

Ziegler, Clementon, N.J., assignors to-American Cyanamid Company, Stamford, Conn., a corporation of Maine No Drawing. Filed Oct. 19, 1967, Ser. No. 676,633 Int. Cl. C07c 87/66 US. (:1. 260-501.1 1 Claim ABSTRACT OF THE DISCLOSURE This disclosure describes a process for the resolution of racemic a-hydroxy-5,,B-dimethyl-'y-butyrolactone by converting the racemic lactone into the or 1- (1-naphthyl)ethyl amine salts of the and (m dihydroxy-;3,;3-dimethylbutyric acids, separating the salts by fractional crystallization, and then converting the separated salts into the optical isomers and u-hydroxy-fi,5-dimethyl-v-butyrolactone.

BRIEF SUMMARY OF THE INVENTION DETAILED DESCRIPTION OF THE INVENTION The symbols and are used to designate the optical isomers and refer to the direction of rotation of polarized light by the isomers. These symbols are used in preference to the designation dextro (or d) and laevo (or l) because the latter are used to denote the absolute optical configuration of the compounds involved. The lactone gives rise to the acid and vice versa. The lactone is a starting material in the synthesis of d-pantothenic acid, a growth promoting substance. The lactone is reacted with fi-alanine or its esters to form the d-pantothenic acid.

It has been discovered in accordance with the present invention that 1-(1-naphthyl)ethyl amine or 1-(1-naphthyl)ethyl amine can be used to resolve racemic a hydroxy -p,,3 dimethyl-y-butyrolactone. Furthermore, 1-(l-naphthyl)ethyl amine or l-(l-naphthyl) ethyl amine can be reacted directly with the racemic lactone in water with the resultant opening of the ring to produce the corresponding base acid salt and base acid salt or base acid salt and base acid salt, respectively. Thereafter, the salts can be separated from one another and from any unresolved racemic lactone by fractional crystallization from the aqueous solution. It is a distinct advantage of the present invention that the resolution of the racemic lactone can be accomplished in an aqueous medium without the use of organic solvents. It is another advantage of the present invention that only about half as much or l-( l-naphthyl)ethyl amine as the more commonly used resolving agents, such as quinine and brucine, is required to effect resolution. Furthermore, the and 1-(1-naphthyl)ethyl amines are much less expensive than the more commonly used alkaloids resolving United States Patent O ice agents such as quinine, quinidine, cinchonine, conchonidine, strychnine and brucine.

In practicing the process of the present invention racemic m-hydroxy-fl,;8-dimethyl-v-butyrolactone may be reacted directly in water solution with l-(l-naphthyl) ethyl amine or l-(1-naphthyl)ethyl amine to form a mixture of thev diastereoisomeric salts. This reaction is preferably carried out at a temperature of from about 50 C. to about C. and employing about 500 ml. of aqueous solution per mole of lactone used. When one molar equivalent of 1-(1-naphthy1)ethyl amine is employed per mole of racemic lactone, a mixture of l-(1-naphthyl)ethyl amine a,'y-dihydroxy-fl,fl-dimethylbutyrate salt and l-(l-naphthyDethyl amine a,' -dihydroxy-p,fl-dimethylbutyrate salt is obtained. The latter crystallizes from the aqueous solution upon cooling and is removed by filtration whereas the former may be recovered from the filtrate upon evaporation of the aqueous solvent. When one molar equivalent of 1-( l-naphthyl)ethyl amine is employed per mole of racemic lactone, a mixture of l-( l-naphthyl)ethyl amine a,'y-dihydroxy-B,;3-dimethylbutyrate salt and 1- (l-naphthyl)ethy1 amine a,'y-dihydroxy-fi, 8-dimethylbutyrate salt is obtained. The former crystallizes from the aqueous solution upon cooling and is removed by filtration whereas the latter may be recovered from the filtrate upon evaporation of the aqueous solvent. When one-half molar equivalent of 1-( l-naphthyDethyl amine is employed per mole of racemic lactone, the l-(l-naphthyDethyl amine a,'y-dihydroxy- 3,fl-dimethylbutyrate salt crystallizes from the aqueous solution upon cooling leaving the lactone in the supernate. When one-half molar equivalent of 1-(1- naphthyl)ethyl amine is employed per mole of racemic lactone, the 1-(1-naphthyl)ethyl amine 05/)- dihydroxy-fl,fl-dimethylbutyrate salt crystallizes from the aqueous solution upon cooling leaving the lactone in the supernate.

In every case, the diastereoisomeric salt which crystallizes from the aqueous reaction solution upon cooling, and is removed by filtration, is added to a water solution of suificient sodium hydroxide (or potassium hydroxide) to split the diastereoisomeric salt into the free amine base and the sodium (or potassium) salt of the oz,'y-dihydroxy-}8,;8-dimethylbutyric acid. This reaction occurs rapidly at room temperature and the 1-(1-naphthyl)ethyl amine is then removed by extraction with chloroform or any suitable organic solvent immiscible with water since 1-(1-naphthyl)ethyl amine is soluble in substantially all organic solvents. After removal of the 1-( l-naphthyl) ethyl amine, the aqueous railinate is acidified to a pH of approximately 1.0 with a mineral acid (concentrated hydrochloric acid, 50% sulfuric acid, etc.) and then allowed to stand at room temperature for a period of time sufficient to lactonize the hydroxy acid. After the lactone is reconstituted, it is extracted from the aqueous raffinate with a suitable organic solvent such as chloroform, methylene chloride, diethyl ether, benzene, carbon tetrachloride, and the like. The extracts are then combined, dried, and the organic solvent removed by distillation. The

crude lactone thus obtained may then be further purified by successive recrystallizations from methyl isobutyl ketone. It is to be noted that in the above recovery procedure the 1-(1-naphthyl)ethyl amine a,'y-dihydroxy-(LB-dimethylbutyrate salt gives rise to the lactone whereas the 1-( l-naphthyl)ethyl amine a,y-dihydroxy-;8,;8-dimethylbutyrate salt gives rise to the lactone.

Instead of the direct reaction of or 1-(1- naphthyl)ethyl amine with the racemic lactone, anionic salts of the amines may be interacted with cationic salts of the racemic a,' -dihydroxy-fl,/i-dimethylbutyric acid in aqueous solution. Suitable anionic salts of the or 1-(l-naphthyl)ethyl amine are, for example, the hydrochloride, hydrobromide, nitrate, sulfate, phosphate, etc. which may be readily prepared by treating the amines with one equivalent of the appropriate acid in water solution. Suitable cationic salts of racemic a,'y-dihydroxyfl,fl-dimethylbutyric acid are, for example, the sodium salt, potassium salt, magnesium salt, etc. which may be readily prepared by treating racemic a-hydroxy-p,;3-dimethyl-y-butyrolactone with one equivalent of the appropriate cation hydroxide in water solution. It is to be preferred, however, that the inorganic salt obtained by this double decomposition reaction be water soluble and thus not precipitate with the water insoluble diastereoisomeric salt. In all other respects the conditions of time, temperature, concentration, proportions of reactants, etc. are the same as for the direct reaction of the or amine bases with the racemic lactone and similar results are obtained.

The invention will be described in greater detail in conjunction with the following specific examples.

EXAMPLE 1 Preparation of a-hydroxy-fi,;S-dimethyl-' butyrolactone To 17 grams of 1-(1-naphthyl)ethyl amine in 20 ml. of water was added 8.2 ml. of hydrochloric acid (specific gravity 1.19) to form a solution of the amine hydrochloride. To this was added 65 ml. of a solution of racemic sodium, a,'y-dihydroxy-[3,fl-dimethylbutyrate, prepared from 26 grams of the racemic whydroxy-fifi-dimethyl-' -butyrolactone, both solutions being warmed to 60 C. On cooling, the solution deposited crystals of 1-(l-naphthyl)ethyl amine a,'y-dihydroxy- 5,,8-dimethylbutyrate salt which were removed at 4 C. and washed with ice-water. These crystals were suspended EXAMPLE 2 Preparation of u-hydroxy-fl,/3-dimethyl-ybutyrolactone The procedure of Example 1 was repeated using 17 grams of 1-(1-naphthyl)ethyl amine in place of the l-(l-naphthyl)ethyl amine, resulting in a yield of 12.5 grams of product having a specific rotation in water of 36.

What is claimed is:

1. The compound 1-(1-naphthyl)ethyl amine a,' -dihydroxy-fl,fl-dimethylbutyrate.

References Cited UNITED STATES PATENTS 3,185,710 5/1965 Dunkel 260-3436 3,000,947 9/1961 Bottoms 260501.l

OTHER REFERENCES Ozegowski et al.: Chemical Abstracts, vol. 55, col. 390-391 (1961).

LEON ZITVER, Primary Examiner M. W. GLYNN, Assistant Examiner US. Cl. X.R. 260343.6 

